U.S. patent application number 15/524519 was filed with the patent office on 2017-11-09 for secondary base station bearer change.
This patent application is currently assigned to Alcatel Lucent. The applicant listed for this patent is ALCATEL LUCENT. Invention is credited to Philippe Godin, Sudeep Palat, Chandrika Worrall.
Application Number | 20170325133 15/524519 |
Document ID | / |
Family ID | 52016001 |
Filed Date | 2017-11-09 |
United States Patent
Application |
20170325133 |
Kind Code |
A1 |
Worrall; Chandrika ; et
al. |
November 9, 2017 |
SECONDARY BASE STATION BEARER CHANGE
Abstract
A secondary base station method, secondary base station, master
base station method, master base station and computer program
products are disclosed. The secondary base station method
comprises: upon it being determined that the secondary base station
is to perform a protocol layer re-establishment, permitting
continued transmission of data packets to user equipment over the
secondary base station bearer. In this way, service interruption
can be minimized since pending data packets may continue to be
transmitted while the re-establishment takes, which minimizes
service interruption and reduces the number of data packets which
will need to be retransmitted.
Inventors: |
Worrall; Chandrika;
(Swindon, GB) ; Palat; Sudeep; (Swindon, GB)
; Godin; Philippe; (Nozay, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALCATEL LUCENT |
Boulogne-Billancourt |
|
FR |
|
|
Assignee: |
Alcatel Lucent
Boulogne Billancourt
FR
|
Family ID: |
52016001 |
Appl. No.: |
15/524519 |
Filed: |
October 13, 2015 |
PCT Filed: |
October 13, 2015 |
PCT NO: |
PCT/EP2015/073631 |
371 Date: |
May 4, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/0027 20130101;
H04W 36/0069 20180801; H04W 36/18 20130101; H04W 36/0055
20130101 |
International
Class: |
H04W 36/00 20090101
H04W036/00; H04W 36/18 20090101 H04W036/18; H04W 36/00 20090101
H04W036/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2014 |
EP |
14306791.6 |
Claims
1. A secondary base station method, comprising: upon it being
determined that said secondary base station is to perform a
protocol layer re-establishment, permitting continued transmission
of pending data packets to user equipment over a secondary base
station bearer.
2. The method of claim 1, wherein said protocol layer
re-establishment is due to said secondary base station bearer being
moved to another base station.
3. The method of claim 1, wherein said protocol layer
re-establishment is due to layer 2 protocol layers of said
secondary base station being re-established.
4. The method of claim 1, wherein said permitting comprises
permitting continued transmission of pending data packets to user
equipment over all secondary base station bearers of said secondary
base station.
5. The method of claim 1, wherein said permitting comprises
permitting continued transmission until a trigger occurs which
ceases transmission.
6. The method of claim 5, comprising generating said trigger.
7. The method of claim 5, wherein said trigger comprises a message
received from a master base station.
8. The method of claim 1, comprising transmitting an indication of
data packets successfully delivered to said user equipment over
said secondary base station bearer until said transmission
ceased.
9. The method of claim 1, comprising transmitting an indication of
data packets successfully delivered to said user equipment over
each secondary base station bearer until said transmission on said
secondary base station bearer ceased.
10. The method of claim 8, wherein said indication indicates a last
successfully delivered sequential data packet for that secondary
base station bearer.
11. The method of claim 8, wherein said indication indicates any
successfully delivered subsequent non-sequential data packets for
that secondary base station bearer.
12. A secondary base station, comprising: logic operable, upon it
being determined that said secondary base station is to perform a
protocol layer re-establishment, to permit continued transmission
of pending data packets to user equipment over said secondary base
station bearer.
13. A master base station method, comprising: upon it being
determined that a secondary base station is to perform a protocol
layer re-establishment, awaiting an indication of data packets
successfully delivered to user equipment over a secondary base
station bearer until transmission ceased.
14. A master base station, comprising: logic operable, upon it
being determined that a secondary base station is to perform a
protocol layer re-establishment, to await an indication of data
packets successfully delivered to user equipment over a secondary
base station bearer until transmission ceased.
15. A computer program product operable, when executed on a
computer, to perform the method of claim 1.
16. A computer program product operable, when executed on a
computer, to perform the method of claim 13.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a secondary base station
method, secondary base station, master base station method, master
base station and computer program products.
BACKGROUND
[0002] Wireless telecommunication systems are known. In such
systems, network connectable devices known as user equipment (for
example, mobile telephones or wireless devices such as iPads or
other similar tablets) are operable to communicate with base
stations provided by network providers.
[0003] In known wireless telecommunication systems, radio coverage
is provided to network connectable devices within geographical
areas, each known as a cell. A base station is located in each cell
to provide radio coverage. Typically, network connectable devices
in each cell are operable to receive information and data from a
base station and to transmit information and data to a base
station.
[0004] Network connectable devices roam through the wireless
communication system. A number of base stations are typically
provided and are distributed geographically in order to provide a
wide area of coverage to network connectable devices.
[0005] If a network connectable device is within an area served by
a base station, communications may be established between user
equipment and the base station over associated radio links. Each
base station typically supports a number of sectors or cells within
the geographical area of radio coverage or service. Typically, a
different antenna provided at a base station supports each
associated sector or cell. Each base station often has multiple
antennas.
[0006] Traditional base stations provide coverage in relatively
large geographical areas and such cells are often referred to as
macro cells.
[0007] In some cases, "dual connectivity" may be offered, such that
a network connectable device is configured to allow communication
with two base stations; a master base station and secondary base
station. Those two base stations may, for example, comprise two
macro cell base stations or a macro cell base station and a small
cell base station. A number of dual connectivity implementations
may be configured and each may offer different benefits.
[0008] Although dual connectivity deployments may offer advantages,
unexpected consequences of such deployments may occur. It is
desired to address those consequences.
SUMMARY
[0009] According to a first aspect, there is provided a secondary
base station method, comprising: upon it being determined that the
secondary base station is to perform a protocol layer
re-establishment, permitting continued transmission of data packets
to user equipment over the secondary base station bearer.
[0010] The first aspect recognizes that dual connectivity involves
a user equipment connecting to a master base station (MeNB) and
secondary base stations (SeNB) at the same time. From a Radio
Resource Control (RRC) signalling over radio point of view, there
are two main signalling procedures which control the configuration
of bearers for the transmission of data packets to the user
equipment when operating in dual connectivity. The first is an RRC
parameter reconfiguration which does not involve the
re-establishment of the layer 2 protocol stack in the secondary
base station. The second is a secondary base station cell group
(SCG) change procedure which requires the re-establishment of the
layer 2 protocol stack at the secondary base station; the
SCG-Packet Data Convergence Protocol (PDCP) layer is
re-established, the SCG-Radio Link Control (RLC) layer is
re-established, the SCG-Medium Access Control (MAC) is reset and
the SCG-Physical layer (PHY) is released. The first aspect also
recognizes that when a protocol layer re-establishment is required,
the time taken to effect the change may be comparatively long due
to non-ideal backhaul characteristics of the network interfaces,
which may interrupt communication with the user equipment.
[0011] Accordingly, a method is provided. The method may be for a
secondary base station. The method may comprise that upon or when
it is determined, detected or established that the secondary base
station is to re-establish protocol layers, transmission of any
pending data packets may be continued over the secondary base
station bearer. In this way, service interruption can be minimized
since pending data packets may continue to be transmitted until the
re-establishment takes place, which minimizes service interruption
and reduces the number of data packets which will need to be
retransmitted.
[0012] In one embodiment, the method comprises continuing
transmission of data packets to user equipment over the secondary
base station bearer.
[0013] In one embodiment, said protocol layer re-establishment is
due to said secondary base station bearer being moved to another
base station.
[0014] In one embodiment, said protocol layer re-establishment is
due to layer 2 protocol layers of said secondary base station being
re-established.
[0015] In one embodiment, the permitting comprises permitting
continued transmission of data packets to user equipment over all
secondary base station bearers of the secondary base station.
Hence, transmission may continue over every bearer for that
secondary base station.
[0016] In one embodiment, the permitting comprises permitting
continued transmission until a trigger occurs which ceases
transmission. Accordingly, when the trigger occurs, the continued
transmission of the data packets may stop.
[0017] In one embodiment, the method comprises generating the
trigger. Accordingly, the secondary base station may itself
generate the trigger.
[0018] In one embodiment, the generating occurs in response to at
least one of resources available to the secondary base station and
bearer condition between the secondary base station and user
equipment. Accordingly, the secondary base station may generate the
trigger due to existing constraints on its resources, which it
considers may be best allocated to a bearer which is not currently
indicated as being about to be moved, or because the efficiency of
the bearer about to be moved is low due to poor radio
conditions.
[0019] In one embodiment, the trigger comprises a message received
from a master base station. Accordingly, the master base station
may indicate to the secondary base station that the continued
transmission is to be stopped.
[0020] In one embodiment, the message triggers a period after which
transmission is to cease. Accordingly, the stopping of the
transmissions may occur after a defined period.
[0021] In one embodiment, the message comprises at least one of a
secondary base station modification confirm message and a user
equipment context release message. It will be appreciated that any
suitable message may be used.
[0022] Embodiments also recognize that the SCG change procedure
will likely result in data packet loss unless a mechanism is
provided to prevent this. This is particularly the case because
when the SCG change is performed, all bearers which are offloaded
via the secondary base station are impacted due to the
re-establishment of the entire SCG-PDCP, SCG-RLC and the re-set of
the SCG-MAC. This is particularly problematic when operating in a
split bearer dual connectivity mode, since this is an
RLC-Acknowledgement Mode (AM) and lossless communication should be
ensured for traffic mapped onto RLC-AM bearers. When a split bearer
is reconfigured as a master base station cell group (MCG) bearer or
moved to another secondary base station, data which has been sent
to the secondary base station but not yet successfully delivered to
the user equipment must be sent again. Hence, the master base
station needs to know which packets were successfully delivered to
the user equipment to know which data packets need to be
retransmitted. Hence, embodiments recognize that a technique is
required to prevent loss of traffic mapped onto a split bearer upon
the SCG change or where a change in bearer type occurs from a split
to a MCG bearer. Although techniques exist for assisting in the
prevention of loss data packets, these rely on a PDCP status report
from the user equipment. However, such a status report is optional
and so cannot be relied upon. When the PDCP status report is not
used, the network would need to retransmit the first unconfirmed
in-sequence data packet. This confirmation is based on the RLC
acknowledge mode acknowledgements. However, for the split bearer in
the secondary base station, the master base station does not have
any RLC acknowledge mode acknowledgment information from the
secondary base station and so this approach is also not suitable
for split bearers.
[0023] Accordingly, in one embodiment, the method comprises
transmitting an indication of data packets successfully delivered
to the user equipment over the secondary base station bearer until
the transmission ceased. Hence, the master base station is provided
with an indication from the secondary base station itself of those
data packets which were successfully delivered to the user
equipment.
[0024] In one embodiment, the method comprises transmitting an
indication of data packets successfully delivered to the user
equipment over each secondary base station bearer until the
transmission on the secondary base station bearer ceased.
Accordingly, the master base station will determine those data
packets provided to the secondary base station which have not been
successfully delivered.
[0025] In one embodiment, the indication indicates a last
successfully delivered sequential data packet for that secondary
base station bearer. This provides a particularly efficient
technique for indicating those data packets which have been
delivered and therefore which may not be delivered and need to be
retransmitted.
[0026] In one embodiment, the indication indicates any successfully
delivered subsequent non-sequential data packets for that secondary
base station bearer.
[0027] In one embodiment, the indication is provided over a master
base station-to-secondary base station interface. One such
interface is the X2 interface.
[0028] In one embodiment, it is determined that the secondary base
station is to perform the change in the secondary base station
bearer in response to at least one of conditions being experienced
by the secondary base station and a message received from a master
base station.
[0029] According to a second aspect, there is provided a secondary
base station, comprising: logic operable, upon it being determined
that the secondary base station is to perform a protocol layer
re-establishment, to permit continued transmission of data packets
to user equipment over a secondary base station bearer.
[0030] In one embodiment, the logic is operable to continue
transmission of data packets to user equipment over the secondary
base station bearer.
[0031] In one embodiment, said protocol layer re-establishment is
due to said secondary base station bearer being moved to another
base station.
[0032] In one embodiment, said protocol layer re-establishment is
due to layer 2 protocol layers of said secondary base station being
re-established.
[0033] In one embodiment, the logic is operable to permit continued
transmission of data packets to user equipment over all secondary
base station bearers of the secondary base station.
[0034] In one embodiment, the logic is operable to permit continued
transmission until a trigger occurs which ceases transmission.
[0035] In one embodiment, the logic is operable to generate the
trigger.
[0036] In one embodiment, the logic is operable to generate the
trigger in response to at least one of resources available to the
secondary base station and bearer condition between the secondary
base station and user equipment.
[0037] In one embodiment, the logic is operable to generate the
trigger in response to a message received from a master base
station.
[0038] In one embodiment, the message triggers a period after which
transmission is to cease.
[0039] In one embodiment, the message comprises at least one of a
secondary base station modification confirm message and a user
equipment context release message.
[0040] In one embodiment, the logic is operable to transmit an
indication of data packets successfully delivered to the user
equipment over the secondary base station bearer until the
transmission ceased.
[0041] In one embodiment, the logic is operable to transmit an
indication of data packets successfully delivered to the user
equipment over each secondary base station bearer until the
transmission on the secondary base station bearer ceased.
[0042] In one embodiment, the indication indicates a last
successfully delivered sequential data packet for that secondary
base station bearer.
[0043] In one embodiment, the indication indicates any successfully
delivered subsequent non-sequential data packets for that secondary
base station bearer.
[0044] In one embodiment, the indication is provided over a master
base station-to-secondary base station interface.
[0045] In one embodiment, the logic is operable to determine that
the secondary base station is to perform the change in the
secondary base station bearer in response to at least one of
conditions being experienced by the secondary base station and a
message received from a master base station.
[0046] According to a third aspect, there is provided a master base
station method, comprising: upon it being determined that the
secondary base station is to perform a protocol layer
re-establishment, awaiting an indication of data packets
successfully delivered to user equipment over a secondary base
station bearer until transmission ceased.
[0047] In one embodiment, said protocol layer re-establishment is
due to said secondary base station bearer being moved to another
base station.
[0048] In one embodiment, said protocol layer re-establishment is
due to layer 2 protocol layers of said secondary base station being
re-established.
[0049] In one embodiment, the method comprises transmitting a
message to the secondary base station to cause the secondary base
station to cease transmission over the secondary base station
bearer.
[0050] In one embodiment, the message triggers a period after which
transmission is to cease.
[0051] In one embodiment, the message comprises at least one of a
secondary base station modification confirm message and a user
equipment context release message.
[0052] In one embodiment, the method comprises receiving an
indication of data packets successfully delivered to the user
equipment over the secondary base station until the transmission
ceased.
[0053] In one embodiment, the indication indicates data packets
successfully delivered to the user equipment over each secondary
base station bearer until the transmission on the secondary base
station bearer ceased.
[0054] In one embodiment, the indication indicates a last
successfully delivered sequential data packet for that secondary
base station bearer.
[0055] In one embodiment, the indication indicates any successfully
delivered subsequent non-sequential data packets for that secondary
base station bearer.
[0056] In one embodiment, the indication is provided over a master
base station-to-secondary base station interface.
[0057] In one embodiment, the method comprises re-transmitting any
undelivered data packets for delivery to the user equipment.
[0058] According to a fourth aspect, there is provided a master
base station, comprising: logic operable, upon it being determined
that the secondary base station is to perform a protocol layer
re-establishment, to await an indication of data packets
successfully delivered to user equipment over the secondary base
station bearer until transmission ceased.
[0059] In one embodiment, said protocol layer re-establishment is
due to said secondary base station bearer being moved to another
base station.
[0060] In one embodiment, said protocol layer re-establishment is
due to layer 2 protocol layers of said secondary base station being
re-established.
[0061] In one embodiment, the logic is operable to transmit a
message to the secondary base station to cause the secondary base
station to cease transmission over the secondary base station
bearer.
[0062] In one embodiment, the message triggers a period after which
transmission is to cease.
[0063] In one embodiment, the message comprises at least one of a
secondary base station modification confirm message and a user
equipment context release message.
[0064] In one embodiment, the logic is operable to receive an
indication of data packets successfully delivered to the user
equipment over the secondary base station until the transmission
ceased.
[0065] In one embodiment, the indication indicates data packets
successfully delivered to the user equipment over each secondary
base station bearer until the transmission on the secondary base
station bearer ceased.
[0066] In one embodiment, the indication indicates a last
successfully delivered sequential data packet for that secondary
base station bearer.
[0067] In one embodiment, the indication indicates any successfully
delivered subsequent non-sequential data packets for that secondary
base station bearer.
[0068] In one embodiment, the indication is provided over a master
base station-to-secondary base station interface.
[0069] In one embodiment, the logic is operable to re-transmitting
any undelivered data packets for delivery to the user
equipment.
[0070] According to a fifth aspect, there is provided a computer
program product operable, when executed on a computer, to perform
the method steps of the first or third aspects.
[0071] Further particular and preferred aspects are set out in the
accompanying independent and dependent claims. Features of the
dependent claims may be combined with features of the independent
claims as appropriate, and in combinations other than those
explicitly set out in the claims.
[0072] Where an apparatus feature is described as being operable to
provide a function, it will be appreciated that this includes an
apparatus feature which provides that function or which is adapted
or configured to provide that function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0073] Embodiments of the present invention will now be described
further, with reference to the accompanying drawings, in which:
[0074] FIG. 1 illustrates a bearer release procedure; and
[0075] FIGS. 2 to 4 illustrate bearer type change procedure of
embodiments.
DESCRIPTION OF THE EMBODIMENTS
[0076] Before discussing the embodiments in detail, first an
overview will be provided. As mentioned above, networks which
support dual connectivity can operate in an arrangement where both
a master base station and a secondary base station support
concurrent transmission of data packets to a single user equipment
connected to those base stations in a dual connectivity mode.
[0077] In one arrangement, a single radio bearer is split after the
PDCP layer within the master base station, with some of the data
packets being provided through the lower layers of the master base
station for transmission to the user equipment, and other data
packets being provided over a master base station to secondary base
station interface (typically the X2 interface), where the data
packets are provided directly to the RLC layer of the secondary
base station for transmission to the user equipment. This split
bearer approach provides for increased resources for communication
with the user equipment and so increases throughput. However, this
split bearer approach also means that should there need to be a
change to the secondary base station cell group bearers, then the
layer 2 of the secondary base station needs to be re-established:
the PDCP layer is re-established, the RLC layer is re-established,
the MAC layer is reset and the physical layer is released.
[0078] For those SCG bearers which are split bearers, lossless
communication needs to be ensured (i.e. no data packets should fail
to be received by the user equipment). However, re-establishing the
layer 2 in the secondary base station could lead to data packets
which have not yet been successfully received by the user equipment
when the re-establishment occurs being lost.
[0079] Accordingly, in embodiments, the secondary base station
continues to transmit data packets it has received to the user
equipment whilst it remains convenient to do so, despite a pending
change to a secondary base station cell group bearer. This is
because the change to the bearer may take some time to perform and
so having the secondary base station continue to transmit data
packets while it can helps to minimize any interruption to the user
equipment.
[0080] Once the change to the secondary base station cell group
occurs, the secondary base station may provide an indication of
those data packets which have been successfully received by the
user equipment. Typically, because the change affects all of the
secondary base station cell group bearers, this indication is
provided for each bearer.
[0081] The master base station then uses the information provided
by the secondary base station in order to ensure that any data
packets which were provided to the secondary base station and which
were not delivered are made available for subsequent delivery to
the user equipment to ensure lossless transmission.
[0082] Accordingly, in embodiments, an SCG change which involves a
layer 2 re-establishment in the secondary base station may be
initiated by either the master base station or the secondary base
station. Many different reasons for performing the SCG change are
possible, which include a primary serving cell change, a radio
bearer type change, a security update, a synchronous parameter
reconfiguration, a decision to re-establish layer 2 protocol
layers, and the like. Depending on the cause or trigger for the SCG
change, the secondary base station may continue communication with
the user equipment over the radio interface even after the
initiation of the SCG bearer change. This is in order to minimize
the service interruption to the user equipment due to the SCG
change, which is more frequent in dual connectivity operation.
[0083] A new trigger is introduced so that the secondary base
station provides to the master base station over the X2 interface
upon the SCG change, the latest transmission/reception status of,
for example, PDCP protocol data units (PDUs) sent to and received
by the user equipment. It will be appreciated that the user
equipment typically provides an acknowledgment for each PDCP PDU
successfully received by it. The master base station then uses the
information provided by the secondary base station in support of
lossless communication for all traffic delivered to the secondary
base station prior to/upon the SCG change. It will be appreciated
that this procedure can also be utilized when a split bearer is
changed to an MCG bearer.
SCG Change
[0084] As mentioned above, many different events may cause a change
to occur to a secondary base station bearer such as, for example, a
primary secondary cell change, a data radio bearer type change, a
security update, a synchronous parameter reconfiguration and a
decision at the secondary base station to re-establish layer 2,
each of which are realized with a secondary base station cell group
change procedure. Even though there are different triggers for the
secondary base station cell group change, a common procedure is
applied.
Data Radio Bearer Type Change Procedures
[0085] Although the embodiments mentioned below are described in
the context of a data radio bearer type change, it will be
appreciated that similar techniques may be used for each of the
said triggers mentioned above leading to the secondary base station
cell group change.
[0086] Consider now a request from the secondary base station to
release the secondary base station portion of the split bearer.
With such a request, the master base station can perform any of the
following procedures: [0087] 1. The master base station can release
the corresponding Evolved Packet System (EPS) bearer; [0088] 2. If
the secondary base station portion of the split bearer is not the
last bearer for the user equipment in the secondary base station,
the master base station may decide to change the bearer type from
being a split bearer to a Master Cell Group (MCG) bearer; [0089] 3.
If the secondary base station portion of the split bearer is the
last bearer for the user equipment in the secondary base station,
then the master base station may release the secondary base station
and move the split bearer to the master cell group bearer; [0090]
4. If the secondary base station portion of the split bearer is the
last bearer for the user equipment in the secondary base station,
then the master base station may configure the bearer to another
secondary base station, and so the secondary base station will
change.
Procedure 1
[0091] FIG. 1 illustrates procedure 1 in more detail. After the
secondary base station transmits the SeNB modification required
with a bearer release request, the master base station decides to
release the EPS bearer. Accordingly, the secondary base station can
stop the delivery of the traffic on the bearer immediately. As the
bearer is released, lossless delivery due to the SCG change is not
a concern. Accordingly, the secondary base station can stop the
user equipment communication on the bearer requested to be released
at any time between step 1 and step 5 in FIG. 1. Because this
procedure involves the release of the EPS bearer, it is likely that
the secondary base station will stop communication on the bearer
immediately.
Procedure 2
[0092] FIG. 2 illustrates procedure 2 in more detail, where the
master base station decides to change the bearer type from spit
bearer to MGC bearer. Accordingly, the secondary base station can
stop the user equipment communication on the bearer requested to be
released or changed at any time between the update of SCG config
including SCG change and the reception of the SeNB modification
confirmed message and the random access procedure at steps 6 or 7.
Typically, the user equipment communication on the bearer is
stopped at the earliest of these events.
Procedure 3
[0093] FIG. 3 illustrates procedure 3 in more detail. The secondary
base station can stop the user equipment communication on the
bearer requested to be released at any time between step 1 and step
5.
Procedure 4
[0094] FIG. 4 illustrates procedure 4 in more detail. The secondary
base station can stop the user equipment communication at any time
between steps 0 and 8.
[0095] As can be seen, in each of these examples, a change occurs
to the secondary base station bearer resulting in that bearer being
moved to another base station. However, transmission of data
packets may be continued for a period after it being determined
that the change to the secondary base station bearer is
required.
Delivery Feedback
[0096] For procedures 2, 3 and 4, lossless delivery of data packet
needs to be guaranteed with the SCG change. Therefore, the
secondary base station is required to provide the latest PDCP
feedback indicating the delivery status of those packets by the
secondary base stations (i.e. the secondary base station provides
successfully delivered PDCP PDU information). The secondary base
station (once it stops sending data to the user equipment)
therefore sends a PDCP sequence number status report to the master
base station. It will be appreciated that this can happen at any
time after message 1 for procedures 2 and 3 and after message 0 for
procedure 4.
[0097] The particular decision of when to stop transmitting data
and when to provide the successful delivery information can vary
from implementation to implementation and may even vary dependent
on the conditions being experienced by the secondary base station,
such as its load or the radio conditions on the bearer being
changed. However, in one example implementation of procedure 2,
when the secondary base station receives the SeNB modification
request message at step 2 indicating an SCG change request from the
master base station, the secondary base station provides the
successfully delivered PDCP PDU information for all the bearers of
the secondary base station at the time that the secondary base
station stops transmission of the traffic to the user equipment for
the affected bearer. Therefore, the SCG change indicator in step 2
can be used as an event trigger to provide the PDCP feedback
information subsequently. However, in procedure 4, there is no
differentiation to the old secondary base station indicating the
master base station decision to change the secondary base station
or to release the EPS bearer. The SCG change indicator should also
be included in the SeNB release confirm message at step 3 informing
the secondary base station by providing a trigger to provide the
latest PDCP feedback information subsequently to enable the master
base station to prevent data loss.
[0098] Hence, in summary, for procedures 2 and 4, when the SCG
change is performed over the radio interface as a result of a
bearer release request from the secondary base station or the
master base station, the master base station indicates the decision
for the SCG change to that secondary base station (which may have
itself requested the bearer release). Upon the reception of the SCG
change indicator, the secondary base station may continue with the
user equipment communication on the bearer for as long as possible
(as mentioned above, the duration is a matter of base station
implementation) and the secondary base station generates the latest
PDCP feedback indicating the transmission status of all the bearers
of the secondary base station once the data communication to the
user equipment is stopped.
[0099] The PDCP feedback status is generated per bearer served by
the secondary base station. It will be appreciated that the data
transmissions on different bearers can be stopped at the same or at
different times. Thus, the PDCP feedback information is provided to
the master base station per bearer at the same or at different
times as triggered by the stopping of the data delivery.
[0100] Accordingly, embodiments provide a method for guaranteed
lossless data delivery on split bearers when an SCG change is
performed. This approach does not rely on the PDCP status delivery
indicator from the user equipment which is an optional procedure.
This helps to prevent possible data loss on the split bearer during
an SCG change and also provides a mechanism for minimizing any
duplicate transmissions.
[0101] A person of skill in the art would readily recognize that
steps of various above-described methods can be performed by
programmed computers. Herein, some embodiments are also intended to
cover program storage devices, e.g., digital data storage media,
which are machine or computer readable and encode
machine-executable or computer-executable programs of instructions,
wherein said instructions perform some or all of the steps of said
above-described methods. The program storage devices may be, e.g.,
digital memories, magnetic storage media such as a magnetic disks
and magnetic tapes, hard drives, or optically readable digital data
storage media. The embodiments are also intended to cover computers
programmed to perform said steps of the above-described
methods.
[0102] The functions of the various elements shown in the Figures,
including any functional blocks labelled as "processors" or
"logic", may be provided through the use of dedicated hardware as
well as hardware capable of executing software in association with
appropriate software. When provided by a processor, the functions
may be provided by a single dedicated processor, by a single shared
processor, or by a plurality of individual processors, some of
which may be shared. Moreover, explicit use of the term "processor"
or "controller" or "logic" should not be construed to refer
exclusively to hardware capable of executing software, and may
implicitly include, without limitation, digital signal processor
(DSP) hardware, network processor, application specific integrated
circuit (ASIC), field programmable gate array (FPGA), read only
memory (ROM) for storing software, random access memory (RAM), and
non-volatile storage. Other hardware, conventional and/or custom,
may also be included. Similarly, any switches shown in the Figures
are conceptual only. Their function may be carried out through the
operation of program logic, through dedicated logic, through the
interaction of program control and dedicated logic, or even
manually, the particular technique being selectable by the
implementer as more specifically understood from the context.
[0103] It should be appreciated by those skilled in the art that
any block diagrams herein represent conceptual views of
illustrative circuitry embodying the principles of the invention.
Similarly, it will be appreciated that any flow charts, flow
diagrams, state transition diagrams, pseudo code, and the like
represent various processes which may be substantially represented
in computer readable medium and so executed by a computer or
processor, whether or not such computer or processor is explicitly
shown.
[0104] The description and drawings merely illustrate the
principles of the invention. It will thus be appreciated that those
skilled in the art will be able to devise various arrangements
that, although not explicitly described or shown herein, embody the
principles of the invention and are included within its spirit and
scope. Furthermore, all examples recited herein are principally
intended expressly to be only for pedagogical purposes to aid the
reader in understanding the principles of the invention and the
concepts contributed by the inventor(s) to furthering the art, and
are to be construed as being without limitation to such
specifically recited examples and conditions. Moreover, all
statements herein reciting principles, aspects, and embodiments of
the invention, as well as specific examples thereof, are intended
to encompass equivalents thereof.
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